Dear Todd,
Serious contamination of powder coatings can occur from contact with silicone-based paints. The defects can take the form of craters or "fish eyes" in the finished coating film. The contact of the silicone with the powder can occur through a number of mechanisms. Mist from a finishing operation involving silicone-based paints can carry long distances and become entrained in the ambient air of a powder coating operation. This mist constitutes airborne contamination. The mist of silicone based paint can also contaminate a powder coating finish by depositing itself on the surface of parts before or during the powder coating process. This problem is referred to as surface contamination. Furthermore, the mist from a silicone base paint can be deposited on air handling equipment surfaces such as filters and thereby be distributed to the ambient air, compressed air and/or finishing surfaces.
Silicone-based products, including silicone-based paints, cause craters in powder coatings due to the inherently large difference in surface tension between the silicone-based paint and the powder coating. Craters form when a region of very low surface tension resides within the melted film of a powder coating. The surface tension of silicone-based paints is typically measured at 15 to 20 dynes per centimeter. The surface tension of powder coatings is typically 40 to 50 dynes per centimeter. This is a large enough discrepancy to cause fish eyes.